A solid imaging device of the three-plate type, in which the spatial pixel shifting method is used, conventionally comprises solid imaging elements (CCD or the like) for respective signals of G (green), B (blue) and R (red), wherein the CCDs are placed in such a manner that the CCDs for R and B, for example, are shifted relative to the CCD for G by one-half of a pixel in a horizontal direction.
According to the placement, it can be interpreted that the subject is imaged by a doubled sampling frequency in the spatial pixel shifting method in comparison to the case where the method is not adopted. Observing the signals obtained from the CCDs for the respective colors, any high frequency component having a frequency which is half the sampling frequency, in other words, a frequency equal to or more than the Nyquist frequency is included as a counterfeit signal called the folding component according to the sampling theorem. Such a placement makes the phases of the R and B signals shifted by 180 degrees relative to the G signal, and makes the phase of the included folding component shifted by 180 degrees in a similar manner.
In the respective signals, the high frequency component including the folding component of each color is replaced with a high frequency component common to each color in which the folding component is reduced as a high frequency component replacement processing in the spatial pixel shifting method. More specifically, a common signal for the respective colors, which is similar to a brightness signal, is generated from the respective color signals, and a high frequency component of the common signal is used as the high frequency component common to the respective colors. The common signal is generated, for example, when the R signal is used to represent the signals of the phases of R and B, and the R signal and the G signal are assigned to the formula of ((G+R)/2). As a result, the folding component included in the G signal and the folding components included in the R and B signals are added with the reverse phases, and the respective folding components are thereby cancelled. The high frequency component of the common signal thus obtained is used for the high frequency component replacing processing in which the high frequency component of the common signal is added to a low frequency component of each color. As a result, the signals each having the high frequency component in which the folding component is reduced can be obtained.
However, in the case where a subject having a high chroma, for example, a subject close to a green color which includes the high frequency component having a frequency equal to or more than the Nyquist frequency, is shot, the signals obtained by the CCDs for R and B are very small in comparison to the signal obtained by the CCD for G. Therefore, it is not possible to cancel the folding component of the high frequency component generated due to the failure of a sampling process in the CCD for G using the signals from the CCD for R and B. As a result, the common high frequency component still includes the folding component, resulting in inconvenience of creating the moire effect.
In order to solve the inconvenience, the signal processing circuit recited in the Patent Document 1 controls the generation of the moire effect by reducing a ratio of the common high frequency component to be added to the low frequency component of each color as the chroma is higher in accordance with the levels of the signals from the CCDs for G and R for generating the common high frequency component.    Patent Document 1: 2004-32514 of the Japanese Patent Applications Laid-Open